Structure and Regeneration Status of Woody Seed Oil Species in Northern Botswana

Abstract

Concerns about energy security and environmental risks have sparked interest in edible and non-edible seed oils as potential renewable feedstocks for biodiesel production. A study was conducted to investigate the population structure and regeneration status of woody seed oil species in the districts of Chobe and Ngamiland. The population structure and regeneration condition of woody seed oil species were studied in 20 × 20 m (400 m2) quadrats spaced 50 m apart along a parallel line transect. Data on the identity of all woody species, the number of all live individuals, and the diameter at breast height (DBH) of individuals with DBH > 2 cm of each woody species were collected in each quadrat. The diversity (Hʹ) and evenness (Jʹ) of woody seed oil species were 1.53, 1.42 and 0.71, and 0.85, 0.73 and 0.51 in Parakarungu, Seronga and Shorobe, respectively. Ximenia caffra was the dominant woody seed oil plant in Shorobe and Seronga, and exhibited an inverted J-shaped curve with continuous diameter classes distribution. Trichilia emetica was only found in Parakarungu, where it was the second dominant species and demonstrated excellent recruitment and regeneration. In Shorobe and Seronga, Croton megalobotrys was the second most dominant species. It had low recruitment, which was most likely due to herbivory and predation on seeds and seedlings. The least prevalent species (Sclerocarya birrea, Schinziophyton rautanenii and Guibourtia coleosperma) had no representation in the intermediate diameter-classes, which might be attributed to the selective removal in these diameter-classes. The examination of the population structure of woody seed oil species indicated variations in patterns of diameter-class distribution, indicating differences in the population dynamics of the species across the study areas. The least dominant species experienced hindered recruitment and regeneration due to herbivory and anthropogenic influences.